In some automotive vehicles a manual clutch is disposed between a flywheel and a manual transmission to disengage an engine from vehicle road wheels when it is necessary to change transmission speeds or brake. Manual automotive clutches generally include a plate and a friction disk that is normally urged by a clutch spring to engage an opposing surface on the flywheel. Over time, the friction disk wears and decreases in thickness. In automotive clutches there is a linkage between a clutch pedal and the clutch plate, which linkage overcomes the bias of the clutch spring when the clutch pedal is pressed to pull the clutch plate away from the flywheel via the clutch linkage. As the friction disk wears and decreases in thickness, the distance that the clutch plate travels in order to insure disengagement of the disk from the flywheel increases. In order to compensate for this increased distance, it is necessary to lengthen the linkage so that the plate engages the disk with sufficient force to avoid slippage. Slippage further accelerates clutch wear and can result in the need for expensive clutch maintenance or clutch replacement.
It is current practice to make manual elongation adjustments in the linkage after wear is detected by the owner/operator. A current technique for alerting the owner/operator of clutch wear is to provide about 1½ to 2 inches of pedal free play at the top of the clutch pedal stroke during manufacture of the vehicle. As the clutch disk wears, pressure plate travel is reduced, which indicates to the owner/operator a need for distance adjustment of pedal travel.
In addition, over-travel during clutch disengagement from the flywheel can damage the clutch pressure plate. In view of these considerations, there is a need for a self-adjusting clutch system requiring minimal operator maintenance and minimal adjustment of pedal free play, while providing adequate engagement during operation to maximize clutch life and to minimize the possibility of clutch plate damage due to overtravel.